A construction machine used for crushing various type of ores of mines, includes various types of parts such as a knife of a crusher, a caterpillar shoe for a conveying machine, a bucket knife, a rail and a rail point. The material for these parts is required to have not only a sufficient strength level as a structural member, but also an excellent abrasive resistance, a shock resistance and a corrosion resistance.
A high manganese cast steel, for example, Hadfield steel (carbon: 1-1.3 weight %, manganese: 11.5-13 wt %) has properties such as exhibiting an austenitic structure at room temperature, a low yield point, a high ultimate tensile strength, and a significant work hardening. Therefore, the hardness and the wear resistance of the steel can be increased by a cold working or surface abrasion. In general, a Hadfield steel is heated to 1050.degree. C. or higher, and then quickly cooled, to make an abrasive resistant and shockresistant tough steel, a surface portion of which has a high hardness and an inside portion of which has a high toughness.
Jap. Pat. Appln. KOKAI Publications. Nos. 54-43818, 57-39158 and 55-53513, disclose an abrasive resistant high manganese cast steel in which crystal grains are refined by adding a small amount of each of the elements for preparing a carbide, such as Ti, V, Cu, Zr, Ce, Mo, W and Nb, and another abrasive resistant high manganese cast steel in which a small amount of spherical carbide is precipitated on the base material of a high carbon-manganese steel.
However, in the former abrasive resistant high manganese cast steel, it is difficult to remarkably improve the abrasive resistance only by fining the crystal grains, and the degree of the improvement is limited.
In the latter abrasive resistant high manganese cast steel, the wear resistance can be improved to a certain degree by enhancing the precipitation of the spherical carbide. However, the austenite matrix itself is not improved but maintained as it is, and therefore it is difficult to obtain a sufficient abrasive resistance while maintaining a required level in shock resistance.
The present invention has been proposed to solve the above-described problems and the object thereof is to provide an abrasive resistant high manganese cast steel having an excellent abrasive resistance and an excellent shock resistance.